A conventional power steering device of this type assists an operation of a steering shaft or a rack shaft with driving force of a motor through a reduction mechanism and a transmission mechanism such as gears or belts.
Since, in such a conventional power steering device, it is impossible to distinguish between a malfunction of the motor or other mechanical systems, such as locking thereof, and a locking of a steering wheel, there may be a case where a current supply to the motor is continued for long enough to heat power elements for controlling the motor to high temperature, causing them to be damaged and/or making steering impossible by such mechanical locking, causing a severe accident to occur.
This invention was made in view of such problems, and an object of this invention is to obtain a motor driven power steering control device capable of preventing a motor and power elements from being damaged by excessive temperature and of making steering wheel operation possible when mechanical locking occurs to thereby assure safe operation of an automobile.